Generally speaking, a microelectromechanical system (“MEMS”) is a highly miniaturized device having both electrical and mechanical components. MEMS devices are typically fabricated on or from a substrate material, such as a silicon wafer or polysilicon material. A variety of long used, well-known techniques form electrical and mechanical structures in the MEMS devices. The mechanical structures of the MEMS are typically very fragile, and can be easily damaged. Furthermore, the mechanical structures of the MEMS are typically very sensitive, and can be easily impeded. Many factors can affect MEMS performance, including dirt, moisture, and even static electricity.
To protect the fragile microstructure, many MEMS devices have a cap secured over substantially all of the MEMS mechanical components. The cap typically forms a cavity with the device die to allow the MEMS structures to move while simultaneously protecting the structures from the operating ambient. The cap thus is bonded onto the MEMS die in such a way that the MEMS structures to be protected are positioned within this cavity. In some applications, this bond is formed so that the device is hermetically sealed against contaminants.